The issue of heat management of LEDs (light emitting diodes) in lamps is known in the art. LED based solutions are less than 100% efficient. The heat that is generated during operation generally leads to temperatures in the application that may deteriorate the system efficacy and may limit the lifetime of the LEDs and/or other components. In order to transfer heat to the ambient, LED devices generally use a metal heat sink. In most LED applications the heat sink and the light emitting area are two separate elements. The size of the heat sink is in general smaller than the total lamp enclosure, limiting the heat transfer to the ambient and thus the thermal performance. In addition, heat sinks are generally relatively heavy and relatively expensive. Furthermore, heat sinks are generally not optically transparent.
U.S. Pat. No. 8,454,185 B2 discloses a liquid-cooled LED lamp having an outer lamp shade, an inner hollow container, and a plurality of LEDs positioned on a substrate in the space between the inner hollow container and the outer lamp shade. Said space is filled with a heat conducting liquid for conducting heat generated by the LED to the outer lamp shade. A disadvantage of this lamp is that measures have to be taken in order to prevent that electrical components will be in direct contact with the heat conducting liquid. Furthermore, heat transfer to the surroundings may be hampered as the LEDs that are present in the liquid may limit circulation of the liquid in the space. Furthermore, materials that are used in the LEDs, for example luminescent materials such as inorganic phosphors, organic phosphors or quantum dots, may be susceptible to degradation in case these materials become in contact with the heat conducting fluid.
The suggested systems thus seem to suffer from thermal management problems which may only be solved (partially) at the cost of optical properties. Vice versa, when optimizing optical properties, thermal management is a problem.